My former audo system was largely analog based on a Lexicon MC8. And of course a good portion of that audio chain was unbalanced. It was also rather complicated with a modified Lexicon MC8 for direct 8 channel analog in for BluRay. The crossover evolved from a tube based Marchand clone to a Berhinger DCX2496 with a DCX214 bass manager - but of course all I/O was analog.
Here are the new system specs:
1) All audio shall be digital up to the final DACs and onto the analog volume controller. I am using pro balanced 110ohm AES interconnects for the discrete audio and 75ohm for the SPDIF AC3 formats.
2) All analog audio shall be balanced at +4dbm - same as pro systems.
3) 16 speaker channels will be provided for. Note that this includes biampping, eg, the LCRs take up 6 channels alone.
4) DACs will be Lucid 88192 units (x2). I got four of these lightly used in an auction deal.
5) Surround proc will be a modified digital out Lexicon MC8.
6) BluRay will be modified Poineer BD05 modified for AES digital output.
7) The DSP unit is based on the MiniDSP product and final analog preamp / volume controller will be DIY. This is my DIY Trinnov! I have dubbed the main DSP unit the "MC16". It generates 16 channels and since Lexicon never went beyond the MC12, I took the MC16 name for myself!
8) Calibration will be done with REW, which the DSP boards do have an interface.
As I will have access to the native DSP chips, I can build filters in firmware specific to my room if needed, a level of flexibility far beyond many off the shelf systems.
Power Amps: (these will remain unchanged for now)
LCR: Biamped Tube amps. 70w PP KT88's for the LCR mids. 10w PP 6V6's for the LCR tweeters.
SUBS (2): Refurbished Phase Linear 700. This 1979 relic has been rebuilt and made more reliable with some current technology.
Surrounds: 5 channel DIY amp based on LM3886 chips, 75w per channel, Sl,Sr,Bl,Br,Bc. These amps are not the highest "audiophile" quality but more than sufficient for surround duty. I plan to add two height channels and will probably just build more of these amps.
Note all amps have +4dbm TRUE balanced inputs. RCA UNBALANCED ANALOG AUDIO CONNECTIONS ARE NO LONGER ALLOWED!
To start I stripped all my direct analog input mods from the MC8 and added a simple 4 channel (equivalent 8 analog channels) AES transmitter board.
The MC8 is therefore stock in it's operation except that he MC8 volume control does not affect the digital outputs. I also discovered some of the Lexicon effects do tweak the individual channel gains. I will have to match that in my gain controller if needed, nothing is ever simple. Basically the MC8 in my HT has been demoted to an AC3/DTS and enhanced 7.1 digital only effects processor for those sources - DVD, Satellite, Media Server. I may still use the analog Zone 2 section for the other house TVs since it has a good 5.1/7.1 mixdown function.
The "VOL16" Unit:
The MiniDSP boards do not provide a good volume control solution. In addition I need a facility to tweak the individual speaker gains for room conditions. The Lexicon MC8 provides for this as do most processors but it's usually done in the analog section. As I am taking direct digital out, I lose this very important feature.I also am in the camp that believes gain control in an audio system is still best done analog. I do respect the opposing views as they have equally good science to back up their claims for digital volume control. As with anything, there are good analog and bad analog gain solutions as well as good and bad digital solutions. I hope to have designed a top notch analog solution here.
So here is the VOL16. This is a 16 channel computer controlled gain controller. It is based on Burr Brown PGA2310 VCA chips coupled with Analog Devices SSM 2141 and SSM2142 audio balanced line driver & receiver chips. These are all very good quality analog chips designed specifically for high end audio. The audio path is simple and clean. All power supplies including the +5v digital power for the CPU are linear, not switch mode. I was a little concerned about the VFD display high voltage inverter causing RFI but I can't see it on the audio signal at all - at least to -106db. Of course being CPU controlled, I have the ability for different presets as well as a plethora of other features which can be added. There is an RS232 port for external control running at 38K baud for fast response.
Main VCA board completed. The 16 relays are for physical mute of the outputs and have a user adjusatble turn on delay time via the front panel menu.
Chassis under construction I found some great rack mount PC chassis for the VOL16 and MC16. I put in a blue custom mounted 20x2 VFD display where the CDROM is intended to go. Silver face seems to be the new fashion over black so I opted for that.
Completed VOL16 under test and software development in my garage lab.
Rear panel. The lone RCA jack is a hardware mute switch closure that can be enabled and disabled on the fly via RS232 as well as an RS232 mute command. Both the external hardware and RS232 mute option action is soft - a very fast fade down so as not to produce clicks. The physical mute relays are only used for power up delay.
Next installment, construction of the MC16 DSP chassis.